Method and apparatus for vibratory grinding



Aug. 25, 1953 N. AHLMANN 2,650,033

METHOD AND APPARATUS FOR VIBRA'IORY GRINDING Filed June 9, 1949 25 24 23 22 z/ a a0 /&

BEARlNG I 5 ROTATES FASTER THAN SHAFTE INVENTOR. b 6 61 MKMM A TOR/V575 Patented Aug. 25, 1953 METHOD AND APPARATUS FOR VIBRATORY GRINDING Nikolai Ahlmann, Copenhagen, Denmark, as-

signor to F. S. Smidth & C0,, New York, N. Y., a corporation of New Jersey Application June 9, 1949, Serial No. 97,950 In Denmark June 14, 1948 5 Claims.

This invention relates to the grinding of material by means of grinding bodies and is concerned mor particularly with a novel method of vibratory grinding and with an apparatus by which the method can be advantageously practiced.

The grinding of material by vibrating a mixture of material and grinding bodies has heretofore been carried out in a resiliently mounted container, which is vibrated by means of oscillating weights supported, for example, on a rotating shaft mounted within the container. In the operation of such apparatus, a small circular or elliptic translatory movement is imparted to the entire charge in the container, and such movement is usually in a vertical plane, so that the charge is repeatedly lifted vertically to a slight extent and then dropped by gravity to the bottom of the container. For the power consumption required, the grinding action thus obtained is not satisfactory because the relative movement of the grinding bodies in the mass moving as a whole within the container is slight and also because the grinding pressures are small, since they are determined by the force of gravity acting on the charge.

In another form of vibratory grinding apparatus, the container for the charge of material and grinding bodies is simultaneously rotated and vibrated and the vibration may be efi'ected by means of oscillating weights, as above mentioned. In such apparatus, the bearings of the shaft supporting the container and on which the weights are mounted, are resiliently supported and again, the grinding action is obtained because of the translatory movement of the entire charge within the container.

In both prior forms of apparatus, the container must be resiliently supported, not only because of the movement produced by th oscillating weights but also in order to prevent transmission of the vibration to surrounding objects. The use of such a resilient mounting and of the oscillating weights in many cases makes such grinding apparatus undesirably complicated.

The present invention is directed to the provision of a method of vibratory grinding, according to which the charge of material and grinding bodies is formed into a layer of substantially uniform thickness and of the shape of a body of revolution, the layer being rotated on its axis while being confined against the action of centrifugal force. The confined layer is then revolved about a fixed axis parallel to and offset from the axis of rotation and at a substantially higher rate than its rate of rotation. While the center of gravity of the layer and its confining means are in the axis of rotation of the layer and that axis is offset from the fixed axis, the layer and confining means are appropriately balanced so that the center of gravity of the layer, the confining means, and the balancing means is in the fixed axis.

The forced vibratory movement of the charge may also be effected by rapidly reciprocating the container for the charg in which event, the center of gravity of the container and the charge lies in a straight line. In such an arrangement, balancing members may be provided to cause the center of gravity of all the moving parts to remain at the same point. If desired, the balancing means may take the form of two grinding vessels arranged to balance one another.

The preferred form of the new apparatus for the practice of the method includes a container of the shape of a body of revolution, which is rotated on its axis at a rate greater than the critical speed, that is, the speed of rotation, at which the charge of material and grinding bodies will accumulate in a uniform layer covering the entire inner surface of the container. As is well known, the critical speed is equal to 54.19 divided by the square root of the radius of the container, expressed in feet. The container is mounted for revolution about a fixed axis oii'set from and paralle1 to the axis of rotation, and the rate at which the container is revolved, may then be between about 10 and 40 times the critical speed of the container. The distance between the axes of rotation and revolution may be of the order of a few millimeters, for example, 2 mm. When the vessel is revolved about the fixed axis at the specified speed, the layer of material and grinding bodies repeatedly moves away from the wall of the container to a slight extent, despite the centrifugal force arising from th rotation of the container itself. As a result, the individual elements of the charge of material and bodies are vibrated against the container wall and are, at the same time, subjected to a great grinding pressure, which may be varied by varying the rates of rotation and revolution.

In the new apparatus described, the container mounted for rotation about its own axis and for revolution about a parallel axis is provided with balancing means, so that the moving parts have a common center of gravity lying in the fixed axis. Under those conditions, it is not necessary to provide a resilient mounting for the container and the construction is thereby simplified.

For a better understanding of the invention, reference may be made to the accompanying drawing, in which Fig. 1 is a vertical view, partly in elevation and partly in section, of a form of apparatus for the practice of the new method; and

Fig. 2 is a sectional view on th line 22 of Fig. 1.

The apparatus shown in the drawing comprises a grinding container ll! of cylindrical section having a closed end II provided with a central hub l2 by which it is mounted on one end of a shaft I3. The shaft is mounted for rotation on an axis I4 in a rotary bearing member 15, which is mounted for rotation on an axi [6 in bearings I! in standards Ill. The bearing memher is provided at one end with a gear I meshing with a pinion on a drive shaft 2| supported in bearings in standards 22 and connected through a coupling 23 to the shaft 24 of a gear box 25. The gear box is driven by a motor 26 through a coupling 21 and the gear box includes a shaft 28 connected by coupling 29 to a torsion shaft 30, which is connected by coupling 3| to shaft l3. Couplings 29, 3| may be of the membrane type.

The rotary bearing member I5 is enclosed Within a casing 32, which forms an extension from casing 33 enclosing the grinding container Ill. Casing 33 has a discharge spout 34 at its lower end and the charge of material and grinding bodies is introduced into container ID, through a feed pipe 35 mounted in an opening of the wall of casing 33 and extending into the open end of container It]. The charge is retained within the container by a flange Illa. In order to balance the container l0, its contents, and shaft l3, a disc 35 is mounted on the rotary bearing member l5 within casing 33, the disc carrying a peripheral flange 3'! weighted at 38.

In the practice of the method by the apparatus described, the shaft I3 and container N! with its contents are rotated at a rate such that the charge 39 of material and grinding bodies within the container collects in a substantially uniform layer on the entire inner surface of the container. The layer thus has the cross-sectional shape of a body of revolution and is confined by the cylindrical wall of the container against the action of centrifugal force. While the shaft 13 and container are thus rotated, the rotary bearing member I5 is rotated at a rate,

which is a multiple of the rate of rotation of the container. A a result, the container and its contents and shaft l3 are revolved at the higher rate about the axis l6, which is the common axis of the assembly of bearing member [5, shaft l3, container l0 and its contents, and the balancing means. During the revolution of the container about fixed axis IS, the axis of rotation l4 of the container has a circular motion about the fixed axis, the radius of such motion being equal to the distance between the axes. The charge of material and grinding bodies has a corresponding circular motion and is thus vibrated against the cylindrical wall of the container.

The mill shown in the drawing is intended primarily for discontinuous grinding but may be operated in such manner that the finished material passes over the edge of flange Illa to escape through outlet 34.

In a mill for continuous operation, the cylindrical wall of container I!) may be formed with outlet grates along flange Hla and this is a desirable construction, when the container is of greater axial length in relation to its diameter than is shown. In such cases, the mill is not of the overhung type but is provided with bearings at both ends, and the ground material may be removed by means of an air current sweeping through the grinding container, and, if desired, passing to an air separator.

The rotation of the grinding container at a rate such that the charge of material and grinding bodies collects in a uniform layer on the entire inner surface of the container, that is, at a rate in revolutions per minute greater than the critical speed, is a feature of the invention which may be advantageously employed in an apparatus of the type having a resiliently mounted container vibrated by oscillating weights. An apparatus of the type illustrated, in which the entire group of moving parts has a common center of gravity in the fixed axis, is of much simpler construction and is, therefore, preferred.

I claim:

1. Apparatus for grinding material by means of grinding bodies, which comprises a vessel for containing a charge of the material and grinding bodies and of the shape of a surface of revolution, a support for the vessel dispoed in the longitudinal axis thereof, a mounting for the support, the mounting being rotatable on a fixed axis passing through the vessel and parallel to and offset from said longitudinal axis, means for balancing the assembly of the vessel, the charge, and the support to cause the center of gravity of the assembly and the balancing means to lie in said fixed axis, and means for positively rotating the support and vessel on the longitudinal axis of the vessel at a speed at least equal to the critical speed of rotation of the vessel and for rotating the mounting on said fixed axis at a higher speed than the speed of rotation of the support and vessel.

2. Apparatus for grinding material by means of grinding bodies, which comprises a vessel for containing a charge of the material and grinding bodie and of the shape of a surface of revolution, a support for the vessel disposed in the longitudinal axis thereof, a mounting for the support, the mounting being rotatable on a fixed axis passing through the vessel and parallel to and offset from said longitudinal axis, means for balancing the assembly of the vessel, the charge, and the support to cause the center of gravity of the assembly and the balancing means to lie in said fixed axis, means for positively rotating the support and vessel on the longitudinal axis of the vessel at a speed at least equal to the critical speed of rotation of the vessel, and means for rotating the mounting on said fixed axis at a higher speed than the speed of rotation of the support and vessel.

3. Apparatus for grinding material by means of grinding bodies, which comprises a vessel for containing a charge of the material and grinding bodies and of the shape of a surface of revolution, the vessel being disposed with its longitudinal axis horizontal, a shaft attached to the Vessel and lying in the longitudinal axis thereof, a bearing member for the shaft, means for supporting the bearing member for rotation on a fixed axis passing through the vessel and parallel to and offset from said longitudinal axis, balancing means attached to the supporting means for causing the center of gravity of the vessel, its contents, the shaft, and the balancing means to lie in said fixed axis, means for positively rotating the shaft and vessel on the longitudinal axis of the vessel at a speed at least equal to the critical speed of the vessel, and means for rotating the bearing member at a higher speed than the speed of rotation of the shaft and vessel.

4. A method of grinding material in a vessel having an inner surface of the shape of a body of revolution, which comprises introducing into the vessel a charge of material and grinding bodies in an amount such that the charge, when spread out in a layer of uniform thickness, covers the inner surface of the vessel, rotating the vessel on its axis at a rate such that the material and grinding bodies are held centrifugally against the inner surface of the vessel in a layer of uniform thickness covering said surface, and subjecting the material and grinding bodies to centrifugal pulsation by revolving the vessel on a fixed axis passing through the vessel and parallel to and offset from the axis of rotation at a rate different from its rate of rotation.

5. A method of grinding material in a vessel having an inner surface of the shape of a body of revolution, which comprises introducing into the vessel a charge of material and grinding bodies in an amount such that the charge, when spread out in a layer of uniform thickness, covers the inner surface of the vessel, rotating the vessel on its axis at a rate such that the material and grinding bodies are held centrifugally against the inner surface of the vessel in a layer of uniform thickness covering said surface, and subjecting the material and grinding bodies to centrifugal pulsation by revolving the vessel on a fixed axis passing through the vessel and parallel to and oifset from the axis of rotation at a rate from about ten to forty times its rate of rotation.

NIKOLAI AHLMANN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 405,810 Wegrnann June 25, 1889 569,828 Herzfeld Oct. 20, 1896 706,102 Pendleton Aug. 5, 1902 1,491,601 Fuller Apr. 22, 1924 1,951,823 Eppers Mar. 20, 1934 2,170,768 Schieferstein Aug. 22, 1939 2,209,344 Matthews July 30, 1940 2,248,526 Francois July 8, 1941 2,469,484 Thiman May 10, 1949 2,540,358 Symons Feb. 6, 1951 FOREIGN PATENTS Number Country Date 24,133 Norway Jan. 12, 1914 490,845 France May 10, 1919 251,956 Switzerland Sept. 1, 1948 

